1. Field of the Invention
The present invention relates to magneto-optical recording media, and more particularly, to a magneto-optical recording medium having a mask layer.
2. Description of the Background Art
The magneto-optical recording medium has attracted much attention as a rewritable and highly reliable recording medium with a high storage capacity and is underway to be reduced to practice as computer memory or the like. Recently, the magneto-optical recording medium with a storage capacity of 6.0 G bytes has been adopted as an AS-MO (Advanced Storage Magneto Optical Disk) standard and is coming into use. A signal is reproduced from such a high density magneto-optical recording medium by an MSR (Magnetically Induced Super Resolution) method, according to which a laser beam is irradiated to transfer a magnetic domain of the recording layer of the magneto-optical recording medium onto the reproducing layer, a detection window is formed at the reproducing layer so that only the transferred magnetic domain can be detected and the transferred magnetic domain is detected based on the formed detection window.
The magnetic domain expansion reproduction technique has been developed, according to which an alternate magnetic field is applied at the time of reproducing a signal from the magneto-optical recording medium and the signal is reproduced by expanding and transferring a magnetic domain of the recording layer onto the reproducing layer using the laser beam and alternate magnetic field, and a magneto-optical recording medium capable of recording and/or reproducing a signal of 14 G bytes using this technique has been proposed.
However, as the recording density increases, a plurality of magnetic domains may be transferred to the reproducing layer at the time of transferring a magnetic domain of the recording layer by irradiating a laser beam, which prevents accurate signal reproduction.
As the recording density increases, when a magnetic domain of the recording layer is transferred onto the reproducing layer by irradiating a laser beam, the direction of magnetization does not quickly change at boundary within the horizontal plane of the magnetic domain transferred to the recording layer and the transferred domain cannot be accurately detected. As the recording density increases, a plurality of magnetic domains to be transferred to the reproducing layer may exist within the diameter of a laser beam spot. As a result, signals cannot be accurately reproduced. These disadvantages are encountered by magneto-optical recording media which reproduce a signal by the MSR method and by the magnetic domain expansion reproduction.
Hirokane discloses a magneto-optical recording medium having a mask layer in xe2x80x9cImprovement of Readout Resolution of MSR Magneto-Optical Disk Using an In-Plane Magnetization Mask Layerxe2x80x9d, a document by Institute of Electrical Engineers of Japan, Magnetics Society, (Nov. 18 to 19, 1997). However, in this magneto-optical recording medium, the recording layer is formed on the mask layer with a non-magnetic layer therebeteween rather than being directly formed on the mask layer.
It is one object of the present invention to provide a magneto-optical recording medium allowing each magnetic domain of the recording layer to be accurately transferred onto the reproducing layer even if the recording density increases, so that the transferred magnetic domain can be accurately detected.
According to the present invention, the magneto-optical recording medium includes a substrate, a reproducing layer, a mask layer and a recording layer. The reproducing layer is formed on the substrate. The mask layer is formed on the reproducing layer, and has a Curie temperature higher lower than a reproducing temperature at the time of irradiating a laser beam and higher than room temperature. The recording layer is directly formed on the mask layer.
In the magneto-optical recording medium, when a laser beam is irradiate, and the temperature is raised, the region of the mask layer within the spot diameter of the laser beam whose temperature has reached the Curie temperature is demagnetized. As a result, the leakage magnetic field of a magnetic domain of the recording layer reaches the reproducing layer through the demagnetized region, and the magnetic domain of the recording layer is transferred to the reproducing layer by magneto-static coupling through the demagnetized region. Also in this magneto-optical recording medium, the recording layer is directly formed on the mask layer, there is no intermediate layer of a non-magnetic material, so that magnetic domains can be accurately transferred from the recording layer to the reproducing layer.
The mask layer is preferably an in-plane magnetization film. Therefore, the region other than the demagnetized region has in-plane magnetization, and therefore the leakage magnetic field of the magnetic domain will not reach the reproducing layer through the mask layer, while conversely, the leakage magnetic field of the magnetic domain of the reproducing layer will not reach the recording layer through the mask layer. As a result, the magnetic domain transferred to the reproducing layer can be readily expanded by an externally applied alternate magnetic field, and a signal in the recording layer can be surely retained.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.